You are using the old V2 version of the Geocoding API, which Google have recently deprecated in favour of the new V3 API. Google suggests to use the new service from now on, and while I have no real experience with the new version, it seems that they have improved the service on various points, especially with the structure of the response. You do not need an API key to use the new service, and you simply need to use a slightly different URL:

You mentioned that you were filtering for placemarks on their accuracy property. Note that this field does not appear anymore in the results of the new Geocoding API, but in any case, I think it was still not very reliable in the old API.

You may want to try to use the bounds and region parameters of the new API, but I still doubt that they will solve your problem.

I believe that the Google Geocoder is a great tool for when you give it a full address in at least a "street, locality, country" format, and it is also very reliable in other formats when it doesn't have to deal with any ambiguities (Geocoding "London, UK" always worked for me).

However, in your case, I would really consider pre-computing all the coordinates of each German locality and simply handle the geocoding yourself from within your database. I think this is quite feasible especially since your application is localized to just one country. Each town in the Wikipedia "List of German Towns" appears to have the coordinates stored inside a neat little <span> which looks very easy to parse:

<span class="geo">47.84556; 8.85167</span>

There are sixteen Neustadts in that list, which may be better than Google's six :)